This invention relates generally to gas turbine engines and, more particularly, to means for modulating cooling airflow to the turbine component portions thereof.
As turbine inlet temperatures have been increased in order to improve the efficiency of gas turbine engines, it has become necessary to provide cooling air to the turbine blades and vanes in order to limit the temperatures of those components to levels which are consistent with the material properties thereof. At the higher operating speed conditions, such as at takeoff, the amount of cooling air that is required is relatively high, whereas during lower temperature operating conditions, such as at idle, there is relatively little, if any, cooling air required for the turbine components. However, for reasons of simplicity and safety, it has not been considered desirable to modulate the flow of cooling air to the turbine components. As a result, since the engine must be designed so as to provide the amount of cooling airflow required for maximum temperature operation, an excess amount of cooling air is provided during other operating conditions so as to thereby reduce the efficiency of the engine during those operating periods.
Generally, modulation of the cooling air by the use of valving has been avoided because of the possible consequences of valve failure. Not only has it been considered necessary that such a valve be fail-free or fail-safe, but also that the logic and equipment needed to operate the valve would also be trouble-free. A further complication is that the airflow path of the engine is often dispersed and buried deep in the engine where it is not readily available for valving.
It is, therefore, an object of the present invention to provide an improved cooling system for a turbine engine.
Another object of the present invention is the provision for improving the efficiency of a turbofan engine by modulating the cooling airflow therein.
Yet another object of the present invention is the provision in a turbomachine for modulating the cooling flow in a practical and safe manner.
Still another object of the present invention is the provision in a turbomachine for a cooling flow modulation system which is economical to manufacture and effective in use.
These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.